The Nature of Human Emotions
Scienceweek, 3 August 2001

Although what we call "emotions" certainly involve significant events in the nervous system, and neural structures strongly associated with emotions have been identified, most advanced textbooks in neuroscience devote only minor space to emotions, and some textbooks avoid the subject completely. There are many reasons for this, and one reason is that despite the scientific attention given to emotions by the archetypical classical biologist Charles Darwin, human emotions (grouped as "affect") are traditionally considered the investigative province of psychology and psychiatry rather than a province of neurobiology. But this attitude is rapidly changing. We certainly know more now about the neurobiological correlates of emotions than we did 50 years ago, and new techniques are making possible important new research.

In general, all emotions are expressed through both physiological changes and stereotyped motor responses, especially responses of the facial muscles. These responses accompany subjective experiences that although not easily described are apparently much the same in all human cultures. Expression of the emotions is closely tied to the autonomic nervous system, and it therefore involves the activity of certain defined brain structures (e.g., brainstem nuclei, hypothalamus, amygdala), as well as autonomic nervous system components (e.g., preganglionic neurons in the spinal cord, autonomic ganglia, peripheral effectors). The brain centers that coordinate emotional responses have been grouped as the "limbic system". At the level of the cerebral cortex, the two hemispheres apparently differ in their governance of the emotions, with the right hemisphere more critically involved than the left hemisphere.

Robert Plutchik (Albert Einstein College of Medicine, US) presents a review of current ideas concerning the nature of human emotions, the author making the following points:

1) The author points out that what we call "cognition" -- the activity of knowing, learning, and thinking, of which emotion is a part -- evolved over millions of years. Charles Darwin (1809-1882) recognized that the process of evolution by natural selection applied not only to anatomic structures but also to the "mind" of an animal and to expressive behavior, a conclusion that led him to write a treatise on emotional expression (The Expression of Emotion in Man and Animals, 1872). Those who have followed Darwin in studying the evolutionary origins of emotions have sought to understand how emotions increase evolutionary fitness for the individual.

2) The author points out that an emotion is not simply a feeling state: emotion is a complex chain of loosely connected events, the chain beginning with a stimulus and including feelings, psychological changes, impulses to action, and specific goal-directed behavior. In other words, feelings do not happen in isolation. They are responses to significant situations in the life of an individual, and often they motivate actions. The author suggests this definition of emotions allows the concept to be generalized to lower animals without difficulty. From his studies of animals, human infants, and human adults, Darwin concluded that expressive behaviors communicate information from one animal to another about what is likely to happen, and emotions therefore affect the chances of survival of the individual demonstrating the behavior. Darwin stated: "Even insects express anger, terror, jealousy, and love by their stridulations."

3) The author (Plutchik) proposes that in general emotions are activated in an individual when issues of survival are raised in fact or by implication. Such situations include threats, attacks, poisonous substances, or the sighting of a potential mate. The effect of the emotional state is to create an interaction between the individual and the event or stimulus that precipitated the emotion. The interaction usually takes the form of an attempt to reduce the disequilibrium and reestablish a state of comparative rest.

Robert Plutchik: The nature of emotions.
American Scientist 89 (2001): 344
Contact: Robert Plutchik: proban@home.com

Source: Scienceweek, 3 Aug 2001